<span>2cos3x = √3 </span><span>cos3x = √3 / 2 </span><span>3x = arccos(√3 / 2) + 2πk, k є Z </span><span>3x = ±π/6 + 2πk, k є Z </span><span>x = ±π/18 + 2πk, k є Z</span>